Min Lai

Facile synthesis of hierarchical porous Co3O4 nanoboxes as efficient cathode catalysts for Li–O2 batteries

Rechargeable Li–O2 batteries with remarkably high theoretical energy densities have attracted extensive attention. However, to enable Li–O2 batteries for practical applications, numerous challenges need to be overcome, e.g. high overpotential, low rate capability, and poor cycling stability. The key factor to tackle these issues is to develop highly-efficient cathode catalysts. Moreover, cathode catalysts with a porous structure and large surface area are favorable in Li–O2 batteries. In this paper, hierarchical porous Co3O4 nanoboxes with well-defined interior voids, functional shells and a large surface area have been facilely synthesized via an ion exchange reaction between Prussian blue analogue nanocubic precursors and OH− at a low temperature (60 °C). The obtained products possess hierarchical pore sizes and an extremely large surface area (272.5 m2 g−1), which provide more catalytically active sites to promote the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as a Li–O2 battery cathode, as well as facilitating the diffusion of oxygen and the electrolyte. The hierarchical porous Co3O4 nanobox cathode shows enhanced discharge capacity, reduced overpotential, improved rate performance and cycle stability, in comparison with the EC-300J carbon cathode. The superb performance of the hierarchical porous Co3O4 nanoboxes, together with the facile fabrication approach, presents an alternative method to develop advanced cathode catalysts for Li–O2 batteries.

Palladium nanoparticle functionalized graphene nanosheets for Li–O2 batteries: enhanced performance by tailoring the morphology of the discharge product

Tailoring the morphology of the cathode discharge product is essential for developing high-capacity and rechargeable lithium oxygen (Li–O2) batteries. In this work, by using functionalized graphene nanosheets (GNSs) with uniformly dispersed palladium nanoparticles (Pd NPs) as the cathode catalyst for the Li–O2 battery, the discharge product of the nano-sized Li2O2 particles formed and homogeneously deposited on GNSs. Through this tailored morphology, the Li–O2 batteries with the Pd functionalized GNS catalyst possessed an increased capacity up to 7690 mA h g−1 at a current density of 0.08 mA cm−2. Meanwhile, reduced charge/discharge overpotentials and good cyclability were obtained.

Monodispersed Ru Nanoparticles Functionalized Graphene Nanosheets as Efficient Cathode Catalysts for O2-Assisted Li–CO2 Battery

In Li–CO2 battery, due to the highly insulating nature of the discharge product of Li2CO3, the battery needs to be charged at a high charge overpotential, leading to severe cathode and electrolyte instability and hence poor battery cycle performance. Developing efficient cathode catalysts to effectively reduce the charge overpotential represents one of key challenges to realize practical Li–CO2 batteries. Here, we report the use of monodispersed Ru nanoparticles functionalized graphene nanosheets as cathode catalysts in Li–CO2 battery to significantly lower the charge overpotential for the electrochemical decomposition of Li2CO3. In our battery, a low charge voltage of 4.02 V, a high Coulomb efficiency of 89.2%, and a good cycle stability (67 cycles at a 500 mA h/g limited capacity) are achieved. It is also found that O2 plays an essential role in the discharge process of the rechargeable Li–CO2 battery. Under the pure CO2 environment, Li–CO2 battery exhibits negligible discharge capacity; however, after introducing 2% O2 (volume ratio) into CO2, the O2-assisted Li–CO2 battery can deliver a high capacity of 4742 mA h/g. Through an in situ quantitative differential electrochemical mass spectrometry investigation, the final discharge product Li2CO3 is proposed to form via the reaction 4Li+ + 2CO2 + O2 + 4e– → 2Li2CO3. Our results validate the essential role of O2 and can help deepen the understanding of the discharge and charge reaction mechanisms of the Li–CO2 battery.

Reversible Tuning of Interfacial and Intramolecular Charge Transfer in Individual MnPc Molecules

The reversible selective hydrogenation and dehydrogenation of individual manganese phthalocyanine (MnPc) molecules has been investigated using photoelectron spectroscopy (PES), low-temperature scanning tunneling microscopy (LT-STM), synchrotron-based near edge X-ray absorption fine structure (NEXAFS) measurements, and supported by density functional theory (DFT) calculations. It is shown conclusively that interfacial and intramolecular charge transfer arises during the hydrogenation process. The electronic energetics upon hydrogenation is identified, enabling a greater understanding of interfacial and intramolecular charge transportation in the field of single-molecule electronics.

RGO/TiO2 nanosheets immobilized on magnetically actuated artificial cilia film: a new mode for efficient photocatalytic reaction

Exploring a proper mode for practical reaction and efficient recycle has been an extensively studied subject in the photocatalysis field. Powder suspension reaction systems and two-dimensional (2D) film reaction systems are insufficient to attain this goal. Herein, we report a systematic study on immobilizing anatase TiO2 nanosheets on the magnetically actuated artificial cilia film by employing reduced graphene oxide (RGO) as the contact medium. The three-dimensional (3D) artificial cilia film is efficient in immobilizing more powder photocatalysts. When the artificial cilia film is actuated by the rotating magnetic field, the rhodamine B (RhB) degradation efficiency can be greatly improved because of the enhanced mass transfer and product desorption efficiencies. Compared to the static state, a three-fold improvement of the photocatalytic activity is obtained when the magnetic field actuation speed is 800 rpm. Furthermore, 83.1% of the photocatalytic activity is retained after 15 circular reactions, indicating its relative stability. Moreover, RGO conductivity and Au surface plasma resonance (SPR) can further improve the RhB degradation efficiency of 9.0% and 8.8%, respectively. Our findings suggest that this new photocatalysis mode is helpful to apply to, and recycle, the high-reactivity powder photocatalysts.

Co3O4 functionalized porous carbon nanotube oxygen-cathodes to promote Li2O2 surface growth for improved cycling stability of Li–O2 batteries

Rechargeable non-aqueous Li–O2 batteries show great potential as an attractive energy storage system due to their ultrahigh theoretical energy density. However, their commercial application is restricted by the large charge overpotential originating from the low conductivity of the discharge product, which thereby results in poor cycle performance. Herein, we develop Co3O4 functionalized porous carbon nanotubes (p-CNT/Co3O4) as an efficient cathode catalyst for Li–O2 batteries. The abundant pore structures of p-CNT can facilitate efficient Li+ and O2 diffusion and provide more buffer interfaces to accommodate the discharge product Li2O2, leading to a high capacity. The functionalization of Co3O4 on the p-CNT surface can significantly enhance the O2 adsorption on the cathode surface and the formation of thin-film Li2O2 proceeds with the surface growth mode, thereby achieving a low charge overpotential. At a current density of 100 mA g−1, the p-CNT/Co3O4 shows an initial discharge capacity of 4331 mA h g−1 with a reduced overpotential of 0.95 V, and is able to work for 116 cycles at 200 mA g−1 with a fixed capacity of 500 mA h g−1.